1. Field of Invention
The invention relates to a vacuum generating apparatus with an electrically driven primary vacuum generator, and a vacuum tube lifter with such a vacuum generating apparatus.
2. Description of Related Art
These vacuum generating apparatuses are used particularly when larger flow volumes of suctioned in air must be evacuated. One example is the handling of objects with what are called vacuum tube lifters. These permit handling in a way that the object to be gripped is held by a gripping device located on a lifting tube, and the lifting tube is shortened by the vacuum that is applied to it. Large volumes must therefore be regularly evacuated from the lifting tube. At the same time it is desirable to provide a sufficiently strong vacuum for the vacuum gripping device of the vacuum tube lifter to assure a firm hold on the object. Vacuum generating apparatuses with electrically driven vacuum generators are also used in systems in which no pneumatic infrastructure, such as a supply of compressed air, is available.
In electrically driven vacuum generators, the vacuum pressure as a rule can be improved only by providing higher RPMs (such as through vacuum pumps) or improved insulation of blower wheels. Such measures are often technically complex and expensive.
On the other hand, items that are called ejectors are known, which are driven with compressed air and which generate a vacuum according to the jet suction pump principle. Ordinarily, an ejector has an ejector nozzle with an inflow opening for the driving compressed air and a capture nozzle with an outflow opening following in the flow path. Between the ejector nozzle and the capture nozzle a vacuum opening is provided, at which a vacuum can be tapped based on a flow from the ejector nozzle to the capture nozzle. To improve the vacuum that is created, what are called multistage ejectors are known, in which several ejectors are connected in series such that the exhaust coming out of the capture nozzle of the first ejector acts as propellant gas for feeding the ejector nozzle of the next ejector in line. EP 1 212 485 A2 shows another type of ejector interconnection. In this case, two ejectors are compactly braced in one housing in a vacuum generating apparatus. A connecting channel is configured in the housing, creating an internal flow connection from the suction connection of the one ejector to the outflow opening on the capture nozzle of the ejector downstream. To the extent that there are several ejector nozzles and capture nozzles of this type combined in one housing, as a result a higher energy efficiency and/or an improved vacuum level can be achieved in comparison with that of a standard ejector. The total apparatus is driven with pressurized fluid.